1. Technical Field
The present disclosure relates to a variable nozzle unit and the like, which adjusts a passage area for (a flow rate of) an exhaust gas to be supplied to a turbine wheel side of a variable geometry turbocharger.
2. Description of the Related Art
In recent years, as described in Japanese Patent Application Publication No. 2009-243431 and Japanese Patent Application Publication No. 2009-243300, various developments have been made on a variable nozzle unit to be disposed inside a turbine housing of a variable geometry turbocharger. A specific configuration of a conventional variable nozzle unit is as described below.
Inside a turbine housing, a first nozzle ring serving as an annular first wall member is disposed concentrically with a turbine wheel. Meanwhile, a second nozzle ring serving as an annular second wall member is provided integrally with the first nozzle ring at a position away axially (in an axial direction of the turbine wheel) from the first nozzle ring, by using multiple connecting pins arranged at intervals in a circumferential direction (a predetermined circumferential direction) The first nozzle ring has a surface (an opposed surface) which is opposed to the second nozzle ring. Likewise, the second nozzle ring has a surface (an opposed surface) which is opposed to the first nozzle ring.
Multiple variable nozzles are disposed between the opposed surface of the first nozzle ring and the opposed surface of the second nozzle ring. The variable nozzles are disposed at regular intervals in the circumferential direction (the predetermined circumferential direction). Each variable nozzle is turnable in forward and reverse directions (opening and closing directions) around a shaft center (a shaft center of a nozzle shaft of the variable nozzle) which is parallel to a shaft center of the turbine wheel. Moreover, a link mechanism is disposed in a link chamber defined and formed on an opposite surface side from the opposed surface of the first nozzle ring. The link mechanism turns the multiple variable nozzles synchronously in the forward and reverse directions. A passage area (a throat area) for an exhaust gas to be supplied to the turbine wheel side is increased when the link mechanism turns the multiple variable nozzles synchronously in the forward direction (the opening direction). On the other hand, this passage area is reduced when the link mechanism turns the multiple variable nozzles synchronously in the reverse direction (the closing direction)
A support ring (an annular support member) having a diameter greater than an outside diameter of the first nozzle ring is provided on the opposite surface from the opposed surface of the first nozzle ring. Meanwhile, an inner edge portion (an inner peripheral edge portion) of the support ring is integrally connected by joining of one end portions of the multiple connecting pins. Multiple pin holes for allowing insertion of the one end portions of the connecting pins are penetratingly formed (formed in a penetrating manner) in the inner edge portion of the support ring at intervals in the circumferential direction (the predetermined circumferential direction). Furthermore, an outer edge portion (an outer peripheral edge portion) of the support ring is attached to a bearing housing in a sandwiched state in cooperation with the turbine housing.